This invention relates to gravimetric fluid density measurement devices.
Fluid density measurement devices are known which are immersed in the fluid and provide a visual reading of the density of the fluid. An example of such a device is described in detail, together with its method of operation, in U.S. Pat. No. 4,353,253. Further devices which can be used for density measurement are described in United Kingdom Patent Specifications 2,015,737 and 1,591,157.
Other devices, also designed for total immersion in the fluid, can be used for remote sensing inside pipelines, oil or water wells, or containers. It is desirable that such devices are made so that they can pass freely through apertures of small diameter, yet, in a non-homogeneous fluid, make readings based on a reasonable displacement volume of fluid.
Devices in common use have suffered from sensitivity to the inclination of the device relative to the vertical, to local gravity effects, and, where the instrument has to be read while moving, to axial acceleration effects.
German Patent Specification DE-A-24 02 400 describes a fluid density measurement device constructed similarly to a balance and which is designed for use above the fluid the density of which is to be measured. United Kingdom Specification GB-A-1,591,157 describes a device for indicating changes in specific gravity of liquid fuel which has two floats and a potentiometer arrangement.
According to this invention there is provided a fluid density measurement device, comprising a buoyancy element mounted for up and down movement about an axis of movement of the device; a weight mounted for up and down movement substantially parallel to the movement of the buoyancy element; a pivotable element mounted for pivotal movement about an axis substantially orthogonal to the movement axis of the device; a first link coupling the buoyancy element to a first location on the pivotable element to convert axial forces on the buoyancy element to rotary forces on the pivotable element tending to rotate the pivotable element; a second link coupling the weight to a second location on the pivotable element to convert axial forces on the weight to rotary forces on the pivotable element such as in use to balance the forces due to the buoyancy element; and means enabling the position of the moveable elements to be determined, whereby when the weight and the buoyancy element are immersed in a fluid the density of which is to be measured, the position of the moveable elements is dependent of the fluid density.
In a preferred embodiment of the invention, the weight is of generally hollow configuration and the buoyancy element moves within the weight. The means enabling the position of the moveable elements to be determined enables the position of the pivotable element to be determined, and may comprise an electrical transducer for providing an electrical output signal representative of the position of the moveable elements. The device preferably includes links for mounting the buoyancy element and the weight, the links being generally orthogonal to the movement axis and comprising a top link and a bottom link for each of the buoyancy element and the weight, the two top links extending in a first direction, and the two bottom links extending in a second direction opposite to the first direction.